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EFFECTS OF LIGHT AND TEMPERATURE 

 ON PLANT GROWTH 



Frits r. Went 



MISSOURI BOTANICAL GARDEN 



An organism's growth is a unique expression of life, utterly different 

 from any properties of the non-living state. Although crystal growth 

 is often compared with the growth of organisms, they have hardly any- 

 thing in common. In crystal growth, pre-existing molecules arrange 

 themselves in patterns which are pre-determined by laws of molecular 

 attraction, and it always involves association of molecules of the same 

 species, unaltered from those in the mother-liquid. In organisms, the 

 specific constituents that make up the cell that must multiply to pro- 

 duce growth ( 1 ) have to be self-duplicating, as far as the basic units 

 are concerned, (2) are dissimilar chemically from the components in 

 the cell medium from which they are assimilated, and, (3) generally 

 have a higher energy content than their components. 



About the first point we have heard much during this symposium, 

 but since I have no information of a biological nature which has any 

 bearing on the self-duplicating aspects of plant growth, I am unable 

 to climb on the bandwagon, and therefore I have to skip this aspect of 

 plant growth. The second and third points, however, seem to me to be 

 of such importance that I want to comment on them. 



Matter loses entropy, and gains orderliness, as it arranges itself 

 in the growing organism. Both of these facts are opposed to the second 

 law of thermodynamics, which rules reactions and processes in the 

 inanimate world. Now in textbooks and in many discussions, respira- 

 tion is usually stressed as a basic prerequisite of growth. This statement 

 is correct, but if let stand by itself, it misses the main point of the 

 growth process. Respiration is a dissimilation process which follows 

 all thermodynamic laws, and consequently it can be understood and 



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